In radial arm saws where many pieces of exactly the same size are often cut, it is the custom to fasten some sort of work piece block on the fence to permit repeated cuts at a minimum of positioning timing. Such blocks are often difficult to position with exactness, and where it is necessary to remove the block for other work, it is difficult to replace them at exactly the same position as previously positioned, as is necessary in doing work requiring fine adjustments, such as cabinet work. It is an object of this invention to provide a means for releasably anchoring a block in position of the fence, and for accurately adjusting a movable block carried by the fence block, to the exact position desired, and providing means for removing said block and replacing same at the exact position desired with a minimum loss of time.